The present invention relates generally to fluid dispensing devices, and particularly to volumetric fluid dispensing devices that dispense a predetermined volume of fluid.
There are many types of fluid dispensing devices currently available. For example, one type of fluid dispensing device that is currently in widespread use is known as a positive displacement filler. Some positive displacement fillers employ a piston and cylinder arrangement to alternately draw and expel a fluid to be dispensed. The piston draws the fluid into the cylinder when it moves in one direction (e.g., a downward stroke), and expels the fluid from the cylinder when it moves in an opposite direction (e.g., an upward stroke). The expelled fluid enters the bottle or container through a tube connected to the cylinder. Other types of positive displacement fillers may employ rotary pumps or diaphragm pumps to alternately draw and expel the fluid.
Another type of fluid dispensing device is known as a time/pressure filler. Generally, these types of devices include a fluid holding tank that maintains the fluid at a relatively constant pressure. Fluid is dispersed into the bottle or container through a length of compressible tubing connected to the tank. A pinch-type valve operates on the tubing to alternately allow and restrict the flow of fluid into the bottle. Operation of the valve may be controlled using a timer, such that the valve opens and closes for predetermined lengths of time. Because the pressure is maintained at a relatively constant level within the reservoir, the same amount of fluid should be dispensed whenever the valve opens.
A third type of fluid dispensing device is known as a volumetric fluid dispensing device. These types of devices first measure a predetermined volume of fluid before dispensing the fluid into the bottle or container. Generally, a fill tube is disposed between the reservoir and the bottle that holds the predetermined volume of fluid to be dispensed. The fill tube may comprise a compressible tube with a pinch-type valve. When the fill tube fills to a specified level, which may be determined by one or more sensors, for example, the pinch-type valve opens to permit the measured fluid to flow through the fill tube and into the bottle or container. Once the fluid is dispensed, the valve closes to stop the flow of fluid until the fill tube once again holds the predetermined amount of fluid.
Another type of volumetric fluid dispensing device uses the net weight of a container or bottle that receives the dispensed fluid. Particularly, the empty bottle or container rests on a balance. As the fluid enters the bottle or container, the balance detects the change in the bottle's weight. When the balance detects that the bottle and fluid have achieved a specified weight, a pinch-type valve closes to stop the flow of fluid into the bottle.
Each of these types of fluid dispensing devices have their advantages, such as speed and/or accuracy, but they also have various disadvantages. Positive displacement fillers, for example, necessarily require that the fluid being dispensed contact the mechanical moving parts of the device. Volumetric fluid dispensing devices use pinch-type valves that tend to warp or degrade the compressible tubing over time. Thus, the fluid being dispensed with these types of devices may become contaminated with undesirable particulate matter. The fluid paths of volumetric fluid dispensing devices cannot be steam sterilized because acceptable materials used in constructing some portions of the dispensing device, such as the fluid reservoir, may melt at autoclave temperatures. Therefore, the user cannot rinse the fluid path with water for injection, and must introduce critical components of the dispensing device to a sterile filling area via an air lock. Additionally, the “hammering” effect of the pinch-type valve could possibly damage some fluids flowing through the compressible tube, for example, protein-based solutions with long molecular chains. Net weight devices are highly accurate, but they require tedious, time-consuming calibration procedures. Further, the fill rate of a net weight device is generally not high enough to warrant their commercial use. Thus, these types of devices are usually relegated to being used as a statistical tool.